Curable compositions

ABSTRACT

Disclosed is a curable composition consisting essentially of (i) a polymerizable double bond-containing resin prepared by introducing a polymerizable double bond-containing group into a polymer containing as a monomer a fluoroalkyl acrylate or methacrylate represented by the formula 
     
         CH.sub.2 ═C(R)--COO(CX.sub.2).sub.m (CF.sub.2).sub.n X (I) 
    
     wherein R is methyl or hydrogen, X is fluorine or hydrogen, m is 1 or 2 and n is an integer of 1 to 12, and (ii) a fluoroalkyl acrylate or methacrylate of the formula (I).

This invention relates to novel curable compositions.

In recent years, technologies of optical fibers have achieved remarkabledevelopments and have found a wide range of practical applications infields such as communications, control systems, various opticallymeasuring techniques and the like. Included among such technologies is,for example, a system in which signals are converted into opticalsignals and the optical signals are transmitted through optical fibersand received as changed to the contemplated type of signals.

An optical fiber is comprised of a core and a cladding surrounding thecore. The core for an optical fiber usually has a refractive index ofabout 1.43 to about 1.60 and is produced by drawing quartz glass or likeglass into threads or made of fibers of polymethyl methacrylate or likeplastics. Generally the core has a diameter of about 5 to about 1000 μm.The cladding is a transparent coating layer of about 3 to about 100 μmthickness formed around the core and having a lower refractive indexthan the core.

Optical signals are transmitted through the core of an optical fiber,repeating total reflection at the interface between the core and thecladding during the transmission. For efficient transmission of opticalsignals through the optical fiber over a long distance withsubstantially no loss, cladding materials for optical fibers arerequired to have properties of being:

(1) lower in refractive index than the core,

(2) excellent in adhesion to the core,

(3) outstanding in flexibility,

(4) not crystalline,

(5) least light-absorbable,

(6) not prone to thermal decomposition and thermal contraction,

(7) scarcely variable in properties depending on temperatures,

(8) high in water resistance and oil resistance, and

(9) outstanding in curability and strength.

Conventional cladding materials include, for example, silicone resins,fluorine-containing resins, boron- or fluorine-containing quartz glassand the like. However, these materials are not satisfactory inproperties. More specifically, silicone resins have the drawbacks ofhaving a high refractive index and being prone to thermal decompositionand thermal contraction, widely variable in properties with temperaturesand poor in curability and strength. Generally it is known to use asfluorine-containing resins non-crosslinkable thermoplastic resins suchas a copolymer of vinylidene fluoride and tetrafluoroethylene (U.S. Pat.No.3,930,103) and a fluoroalkyl methacrylate polymer (U.S. Pat.No.1,039,498). The former polymer remains slightly crystalline in thefiber and thus causes light scattering at the interface between the coreand the cladding, thereby leading to reduction of transmittingproperties, whereas the latter polymer has the disadvantages of beinginsufficient in adhesion to the core and flexibility, and widelyvariable in properties with temperatures. Boronor fluorine-containingquartz glass is unsatisfactory in flexibility and considerablyexpensive, thus economically undesirable.

It is an object o the present invention to provide a novel curablecomposition significantly suitable as a cladding material for opticalfibers.

It is another object of the invention to provide a novel curablecomposition which can overcome the foregoing drawbacks of conventionalcladding materials and which is fully satisfactory in all of theproperties required of cladding materials.

These and other objects of the present invention will become moreapparent from the following description.

The present invention provides a curable composition consistingessentially of (i) a polymerizable double bond-containing resin preparedby introducing a polymerizable double bond-containing group into apolymer containing as a monomer a fluoroalkyl acrylate or methacrylaterepresented by the formula

CH₂ =C(R)-COO(CX₂)_(m) (CF₂)_(n) X (I)

wherein R is methyl or hydrogen, X is fluorine or hydrogen, m is 1 or 2an n is an integer of 1 to 12, and (ii) a fluoroalkyl acrylate ormethacrylate of the formula (I).

We conducted extensive research to develop cladding materials which canovercome the aforesaid drawbacks of conventional cladding materials andwhich are fully satisfactory in all of the properties required ofcladding materials. Our research has revealed the following novelfindings.

(A) The composition consisting essentially of the above-specifiedpolymerizable fluorine-containing unsaturated resin and theabove-specified fluorine-containing unsaturated monomer can readilycrosslink to cure on irradiation of actinic radiation such asultraviolet rays or electron beams.

(B) The cured product of this composition can fully exhibit theforegoing properties required of cladding materials.

The present invention has been accomplished based on these novelfindings.

The polymerizable double bond-containing resin to be used as thecomponent (i) is a polymer containing as a monomer a fluoroalkylacrylate or methacrylate of the formula (I). This resin is prepared byintroducing a polymerizable double bond into the polymer. According tothe-invention, the resin is one prepared usually by reacting a copolymercomprising as the comonomers a monomer of the formula (I) and a vinylmonomer containing a functional group for introducing a polymerizabledouble bond with a compound containing a polymerizable double bond and afunctional group reactive with the functional group of the vinyl monoeerto introduce the polymerizable double bond into the side chain of thecopolymer.

Examples of the vinyl monomer containing a functional group forintroduction of a polymerizable double bond are epoxy group-containingvinyl monomers, hydroxyl group-containing vinyl monomers, carboxylgroup-containing vinyl monomers, isocyanate group-containing vinylmonomers and the like. Preferably the compound reactive with thefunctional group of such vinyl monomer in an ester linkage-formingreaction, urethane linkage-forming reaction or like reaction is selectedfrom the above-exemplified vinyl monomers as the compound containing apolymerizable double bond and a functional group reactive with thefunctional group of the vinyl monomer. For example, when an epoxygroup-containing or hydroxyl group-containing vinyl monomer is used asthe functional group-containing comonomer for the copolymer in theintroduction of a polmmerizable double bond by an ester linkage-formingreaction, a carboxyl group-containing vinyl monomer is used as thecompound to be reacted with the copolymer. Reversely when a carboxylgroup-containing vinyl monomer is used as the comonomer, an epoxygroup-containing or hydroxyl group-containing vinyl monomer is used asthe compound to be reacted therewith. Or when a hydroxylgroup-containing vinyl monomer is used as the comonomer in theintroduction of a polymerizable double bond by a urethanelinkage-forming reaction, a hydroxyl group-containing vinyl monomer isused as the compound to be reacted therewith via a polyisocyanatecompound. Optionally, when an isocyanate group-containing vinyl monomeris used as the comonomer, a hydroxyl group-containing vinyl monomer isused as the compound to be reacted therewith.

It is preferred in preparation of the component (i) to use a fluoroalkylacrylate or methacrylate of the formula (I) wherein n is an integer of 2to 8. Preferred examples of the fluoroalky acrylate or methacrylate ofthe formula (I) are 1,1,3H-tetrafluoropropyl acrylate or methacrylate(n=2), 1,1,5H-octafluoropentyl acrylate or methacrylate (n=4),1,1-tridecylfluoroheptyl acrylate or methacrylate (n=6),1,1,2H,2H-heptadecafluorodecyl acrylate or methacrylate (n=8) and thelike. Among these examples, more preferable are 1,1,3H-tetrafluoropropylacrylate or methacrylate, IH,1,5H-octafluoropentyl acrylate ormethacrylate and 1,1,2H,2Hheptadecafluorodecyl acrylate or methacrylate.

Examples of the epoxy group-containing vinyl monomer are glycidylacrylate or methacrylate, metaglycidyl acrylate or methacrylate and thelike.

Examples of the hydroxyl group-containing vinyl monomer are monoester ofacrylic or methacrylic acid with dihydric alcohol (having 2 to 6 carbonatoms) such as hydroxyethyl acrylate or methacrylate, hydroxypropylacrylate or methacrylate, hydroxybutyl acrylate or methacrylate and thelike; caprolactam-modified acrylate or methacrylate; and like acrylic ormethacrylic monomers.

Examples of tee carboxyl group-containing vinyl monomer are acrylic ormethacrylic acid, 2acryloyloxyethylsuccinic acid,2-methacryloyloxyethylsuccinic acid, 2-acryloyloxyethylmaleic acid,2methacryloyloxyethylmaleic acid, 2-acryloyloxyethylphthalic acid,2-methacryloyloxyethylphthalic acid, 2-acryloyloxyethylhexahydrophthalicacid, 2methacryloyloxyethylhexahydrophthalic acid, β-carboxyethylacrylate, β-carboxyethyl methacrylate and like unsaturated monobasicacids.

Examples of the isocyanate group-containing vinyl monomer are isocyanateethyl acrylate or methacrylate, m-isopropenyl-α,α'-dimethylbenzylisocyanate, a urethane linkage-forming reaction product prepared byreacting the hydroxyl group-containing vinyl monomer with apolyisocyanate compound in substantially equimolar amounts.

Exemplary of the polyisocyanate compound are compounds having at least 2isocyanaee groups in the molecule such as tolyeene diisocyanate,4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylenediisocyanate, lysine diisocyanate,4,4'-methylenebis(cyclohexyl-isocyanate),methylcyclohexane2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate,1,3-(isocyanate-methyl)cyclohexane, isophorone diisocyanate,trimethylhexamethylene diisocyanate, dimeric acid diisocyanate,dianisidine diisocyanate, phenyl diisocyanate, halogenated phenyldiisocyanate, methylene diisocyanate, ethylene diisocyanate, butylenediisocyanate, propylene diisocyanate, octadecylene diisocyanate,1,5-naphthalene diisocyanate, polymethylene polyphenylene diisocyanate,triphenylmethane triisocyanate, naphthylene diisocyanate and the like.Among these examples, tolylene diisocyanate, isophorone diisocyanate andlysin diisocyanate are preferred.

In preparation of the component (i), the copolymer for introducing apolymerizable double bond is prepared usually from the comonomers, i.e.the monomer of the formula (I) and the vinyl monomer containing afunctional group for introducing a polymerizable double bond. Whenrequired, other monomers are usable as an additional comonomer. Examplesof useful other monomers are esters of acrylic or eethacrylic acid withmonohydric alcohol (having 1 to 24 carbon atoms), hydroxyalkyl (having 2to 8 carbon atoms) acrylate or methacrylate, styrene, derivativesthereof, acrylonitrile, methacrylonitrile, vinyl acetate, vinylchloride, etc. These monomers are usable singly or at least two of themcan be used in mixture.

The copolymer to be used in preparation of the component (i) can beprepared by copolymerizing at least one of monomers of the formula (I)and at least one of vinyl monomers containing a functional group forintroducing a polymerizable double bond by conventional polymerizationmethods such as solution polymerization, suspension polymerization orlike methods. In respect of the proportions of the two comonomers, about50 to about 97% by weight, preferably about 70 to about 95% by weight,of the former comonomer and about 3 to about 50% by weight, preferablyabout 5 to about 30% by weight, of the latter comonomer, are used basedon the total weight of the two comonomers in view of the curability andthe refractive index of the composition of the invention. When required,less than 100 parts by weight of other monomer is suitably used per 100parts by weight of the two comonomers as combined. The copolymer has anumber average molecular weight of about 3,000 to about 50,000,preferably about 5,000 to about 30,000.

The component (i) of the composition according to the present inventioncan be obtained by reacting the functional group contained in thecopolymer with the compound containing a polymerizable double bond and afunctional group reactive with the functional group by an esterlinkage-forming reaction, urethane linkage-forming reaction or the liketo introduce the polymerizable double bond into the copolymer. Theamounts of the copolymer and the compound used are not specificallylimited and are suitable if the amounts are such that the unsaturationdegree of the reaction product (the equivalent amount of thepolymerizable double bond per 1,000 of number-average molecular weight)is in the range of about 0.2 to about 3.0, preferably about 0.3 to about2.0. It is desirable that the component (i) prepared by introduction ofthe polymerizable double bond have a number-average molecular weight ofabout 3,100 to about 62,000, preferably about 5,100 to about 31,000.

Preferred examples of the polymerizable double bond-containing resin tobe used as the component (i) are as follows:

(a) a polymerizable double bond-containing resin prepared by reacting acarboxyl group-containing vinyl monomer with a copolymer comprising amonomer of the formula (I) and an epoxy group-containing or hydroxylgroup-containing vinyl monomer as the comonomers to esterify the epoxygroup or hydroxyl group and the carboxyl group,

(b) a polymerizable double bond-containing resin prepared by reacting anepoxy group-containing or hydroxyl group containing vinyl monomer with acopolymer comprising a monomer of the formula (I) and a carboxylgroup-containing vinyl monomer as the comonomers to esterify thecarboxyl group and the epoxy group or hydroxyl group,

(c) a polymerizable double bond-containing resin prepared by reacting ahydroxyl group-containing vinyl monomer with a copolymer comprising amonomer of the formula (I) and a hydroxyl group-containing vinyl monomeras the comonomers via a polyisocyanate compound to form a urethanelinkage, and

(d) a polymerizable double bond-containing resin prepared by reacting ahydroxyl group-containing monomer with a copolymer comprising a monomerof the formula (I) and an isocyanate group-containing vinyl monomer asthe comonomers to form a urethane linkage.

A preferred amount of the compound to be reacted with the copolymer inthe ester linkage-forming reaction for preparation of the resin (a) or(b) is about 0.3 to about 1 mole per mole of the functional group of thecopolymer.

It is preferred to prepare the resin (c), for example, by the followingmethods.

1. A polyisocyanate compound is reacted with the hydroxyl group of thecopolymer in a ratio of about 1 mole of the former per mole of thelatter by a urethane linkage-forming reaction, and then the isocyanategroup of the reaction product is reacted with the hydroxyl group of thehydroxyl group-containing vinyl monomer by a urethane linkage-formingreaction to introduce the polymerizable double bond-containing groupinto the copolymer.

2. A polyisocyanate compound and a hydroxyl group-containing vinylmonomer in equimolar amounts are subjected to a urethane linkage-formingreaction. Then the hydroxyl group of the copolymer and the isocyanategroup of the reaction product are caused to undergo a urethanelinkage-forming reaction to introduce the polymerizable doublebond-containing group into the copolymer. The reaction product is usedpreferably in an amount of about 0.3 to about 1 mole per mole of thehydroxyl group of the copolymer.

It is preferable to prepare the resin (d), for example, by reacting thehydroxyl group-containing vinyl monomer with the isocyanate group of thecopolymer in a ratio of about 0.3 to about 1 mole of the former per moleof the latter by a urethane linkage-forming reaction to introduce thepolymerizable double bond-containing group into the copolymer.

The portion of the component (i) formed from the monomer of the formula(I) in the polymerizable double bond-containing resin serves, incombination with the component (ii), to reduce the refractive index ofthe cured composition (e.g. cured coating layer) and to retain thephysical strength of the cured composition. If the polymerizable doublebond is used in a large amount which falls within the specified range ofthe unsaturation degree, the molecular weight between crosslinksdecreases, thereby resulting in formation of cured composition having anincreased hardness.

The component (ii) is used as a reactive diluent and the fluoroalkylacrylate or methacrylate of the formula (I) is employed as such. Theexamples of the fluoroalkyl acrylate or methacrylate given hereinbeforeas useful in preparation of the component (i) are also usable for thecomponent (ii). Among these examples, 1,IH,2H,2H-heptadecafluorodecylacrylate or methacrylate, 1,1,5H-octafluoropentyl acrylate ormethacrylate and the like are preferred. In the practice of the presentinvention, a portion of the fluoroalkyl acryltte or methacrylate as thecomponent (ii), usually 50% by weight thereof or less, can be replacedby the other monomer as exemplified above in respect of the component(i) or oligomer thereof. Examples of useful oligomers are polyolacrylate or methacrylate, polyester acrylate or methacrylate,polyurethane acrylate or methacrylate, silicone acrylate or methacrylateand like polymerizable double bond-containing oligomers.

The composition of the present invention is prepared by mixing togetherthe components (i) and (ii), the amounts thereof being about 5 to about95% by weight, preferably about 20 to about 80% by weight, of thecomponent (i) and about 5 to about 95% by weight, preferably about 20 toabout 80% by weight, of the component (ii), based on the total weight ofthe two components. If more than 95% by weight of the component (ii)serving as a reactive diluent is used, the composition obtained isundesirable because it tends to have reduced compatibility and to impairthe mechanical properties of the cured composition. However, if lessthan 5% by weight of the component (ii) is used, the resultingcomposition is undesirable because it is likely to have a higherrefractive index and thus to form a cladding with deterioratedproperties.

The curable composition of the invention thus obtained rapidlycrosslinks to cure on irradiation of actinic radiation such asultraviolet rays and electron beams.

When the composition of the invention is cured by irradiation of UVrays, it is preferred to add a photopolymerization initiator to thecomposition. Examples of useful photopolymerization initiators arebenzoin, benzoin methyl ether, benzoin ethyl ether, benzoin n-propylether, benzoin n-butyl ether, benzyl, benzophenone,p-methylbenzophenone, diacetyl, Eosine, Thionine, Michler's ketone,acetophenone, 2-chlorothioxanthone, anthraquinone, chloroanthraquinone,2methylanthraquinone, α-hydroxyisobutylphenone,p-isopropyl-α-hydroxyisobutylphenone,α,α'-dichloro-4phenoxyacetophenone, 1-hydroxy-1-cyclohexylacetophenone,2,2-dimethoxy-2-phenylacetophenone, methylbenzoin formate,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane,dichlorothioxanthone, diisopropylthioxanthone, phenyldisulfide-2-nitrosofluorene, butyroin, anisoin ethyl ether,azobisisobutyronitrile, tetramethylthiuram disulfide, etc. Thesephotopolymerization initiators are usable singly or at least two of themcan be used in mixture. A preferred amount of the photopolymerizationinitiator is about 0.1 to about 10 parts by weight per 100 parts byweight of the total amount of the components (i) and (ii). Aphotopolymerization accelerator can be used in mixture with thephotopolymerization initiator to promote the optically crosslinkingreaction started by the initiator. Examples of usefulphotopolymerization accelerators are triethylamine, triethanolamine,2dimethylaminoethanol and like tertiary amines, triphenylphosphine andlike alkylphosphines, β-thioglycol and like thiols, etc.

Exemplary of the source of UV radiation for curing are a mercury lamp,high-pressure mercury lamp, superhigh-pressure mercury lamp, xenon lamp,carbon arc, metal halide lamp, sunlight, etc. A preferred atmosphere inwhich UV light is irradiated is air or inert gas. When UV light isirradiated in air, it is preferable to use a high-pressure mercury lampas a radiation source. While the radiation dose is not specificallylimited, a proper dose is about 10 to about 2,000 mJ/cm²

The accelerator for electron beams which is used in curing byirradiation of electron beams include, for example, a Cockcroft type,Cockcroft-Walton type, resonance transformer type, transformer type,insulated core transformer type, dynamitron type, linear filament type,broad beam type, area beam type, cathode electron type, high-frequencytype, etc. The dose of electron beams to be irradiated is notspecifically limited insofar as it is sufficient to cure thecomposition. Generally electron beams are irradiated, however, at a doseof about 0.5 to about 20 Mrad at about 100 to about 2,000 KeV. Apreferred atmosphere for irradiation of electron beams is inert gas.

The curable composition of the present invention is remarkably suitablein particular for forming claddings for optical fibers. The claddingformed therefrom is free of the drawbacks of conventional claddingsdescribed hereinbefore and is fully satisfactory in all of theproperties required of claddings. Stated more specifically, a claddingcan be easily produced, for example, by applying the composition of thepresent invention by die coating, immersion or like conventional coatingmethod to a core prepared by drawing a quartz or like material intothreads and irradiating ultraviolet rays, electron beams or like actinicradiation over the layer of the composition to cure the layer rapidly bycrosslinking. Using the cladding thus obtained, a high performanceoptical fiber can be prepared.

The cladding formed from the composition of the present invention canexhibit all the aforesaid properties required of claddings to a fullysatisfactory extent. Since the fluorine content of the composition canbe adjusted to about 25 to about 60% by weight according to the presentinvention, there can be easily obtained therefrom a cladding having arefractive index of about 1.45 to about 1.36 which is so low as to makeit possible to transmit light in a greater amount. Further, the claddingprepared according to the invention is hard and remarkable inflexibility, and scarcely affected by temperatures in respect ofproperties. Consequently, for example, even if one end of optical fibersis fixed, e.g. with an adhesive, the core covered with the cladding isfirmly held. And if the temperature changes, the core therearound isfree from piston-like movement. The cladding is markedly enhanced inflexibility when formed from the composition of the invention having aurethane linkage. Since the composition of the invention providesoptical fibers with a great NA value (NA=abbreviation of numericalaperture, which is given by the equation ##EQU1## wherein N₁ is therefractive index of the core and N₂ is the refractive index of thecladding), light is transmitted therethrough at a larger angle ofincidence with the result that a greater amount of light can betransmitted. With this characteristic, the optical fibers resulting fromthe composition of the invention, when used as light guides forilluminations or decorations, can emit light beams with substantially noloss caused during transmission; when used as an endoscope or like imagefiber devices, it can make the image more clearly visible; and when usedfor communication devices, it can raise the intensity level of opticalsignals sufficiently to reduce the connector loss of light rays andelectricity, thereby making it possible to use, e.g. an inexpensivelight emission diode or photo diode.

The optical fibers with the cladding prepared from the composition ofthe present invention can be suitably used, e.g., as communicationdevices, image guides, light guides and optical fiber-applied measuringinstruments, and in other fields of optical fiber technologies.

Because of its low surface tension and low refractive index, thecomposition of the present invention can be utilized also as a waterrepellents, agents for improving the surface properties, nonreflectivecoats, piezo-electric devices, ultraviolet light resists, electron beamresists, ion exchange membranes and the like. Further the composition ofthe present invention has a good weatherability and is usable also as acoating composition for exterior coating.

The present invention will be described below in greater detail withreference to Preparation Examples illustrative of the preparation of thecomponent (i), Examples and Comparison Examples wherein the parts andpercentages are all by weight unless otherwise specified.

EXAMPLES PREPARATION EXAMPLE 1 Preparation of component (i)-I

A 2l 4-necked flask was charged with 60 parts of methyl isobutyl ketoneand 60 parts of metaxylene-hexafluoride and the mixture was heated to110° C. Added dropwise thereto were 170 parts of1,1,2H,2H-heptadecafluorodecyl acrylate, 30 parts of glycidylmethacrylate and 6 parts of t-butylperoxy-2-ethyl hexanoate through adropping funnel over a period of 3 hours after which the mixture wassubjected to aging for 1 hour. Then added dropwise thereto were 1 partof t-butylperoxy-2-ethyl hexanoate and 13 parts of methyl isobutylketone over a period of 1 hour. Thereafter the mixture was subjected toaging for 7 hours, giving a copolymer having a number-average molecularweight of about 15,000. To the copolymer thus obtained were added 0.1part of hydroquinnne, 1 part of triethylamine and 16 parts of acrylicacid and the mixture was maintained at a temperature of 110° C. for 5hours, producing an acryloyl group-containing resin having anumber-average molecular weight of 16,000 and an unsaturation degree of1.0. The resin solution thus prepared was dried at 40° C. under reducedpressure to remove the solvent, giving a resin having a solids contentof 100%.

PREPARATION EXAMPLE 2 Preparation of component (i)-II

In the same manner as in Preparation Example 1, 6 parts of acrylic acidwas reacted with a copolymer comprising 190 parts of1,1,5H-octafluoropentyl acrylate and 10 parts of glycidyl methacrylate,giving an acryloyl group-containing resin having a number-averagemolecular weight of about 16,000 and an unsaturation degree of 0.4 whichwas dried in the same manner as in Preparation Example 1, producing aresin having a solids content of 100%.

PREPARATION EXAMPLE 3 Preparation of component (i)-III

In the same manner as in Preparation Example 1, 20 parts of acrylic acidwas reacted with a copolymer comprising 80 parts of1,1,2H,2H-heptadecafluorodecyl acrylate, 80 parts of1,1,5H-octafluoropentyl acrylate and 40 parts of glycidyl methacrylate,giving an acryloyl group-containing resin having a number-averagemolecular weight of about 20,000 and an unsaturation degree of 1.3 whichwas dried in the same manner as in Preparation Example 1, producing aresin having a solids content of 100%.

PREPARATION EXAMPLE 4 Preparation of component (i)-IV

A 2l 4-necked flask was charged with 60 parts of methyl isobutyl ketoneand 60 parts of metaxylene-hexafluoride and the mixture was heated to110° C. Added dropwise thereto were 170 parts of1,1,2H,2H-heptadecafluorodecyl acrylate, 20 parts of acrylic acid and 6parts of t-butylperoxy-2-ethyl hexanoate through a dropping funnel overa period of 3 hours after which the mixture was subjected to aging for 1hour. Then added dropwise thereto were 1 part of t-butylperoxy-2-ethylhexanoate and 13 parts of methyl isobutyl ketone over a period of 1hour. Thereafter the mixture was subjected to aging for 7 hours, givinga copolymer having a number average molecular weight of about 14,000. Tothe copolymer thus obtained were added 0.1 part of hydroquinone, 1 partof triethylamine and 35 parts of glycidyl methacrylate and the mixturewas maintained at a temperature of 110° C. for 5 hours, producing anacryloyl group-containing resin having a number-average molecular weightof 15,000 and an unsaturation degree of 1.1. The resin solution thusprepared was dried at 40° C. under reduced pressure to remove thesolvent, giving a resin having a solids content of 100%.

PREPARATION EXAMPLE 5

Preparation of component (i)-V

In the same manner as in Preparation Example 4, 10 parts of glycidylmethacrylate was reacted with a copolymer comprising 190 parts of1,1,5Hoctafluoropentyl acrylate and 7.5 parts of methacrylic acid,giving an acryloyl group-containing resin having a number-averagemolecular weight of about 17,000 and an unsaturation degree of 0.4 whichwas dried in the same manner as in Preparation Example 4, producing aresin having a solids content of 100%.

PREPARATION EXAMPLE 6 Preparation of component (i)-VI

In the same manner as in Preparation Example 4, 80 parts of glycidylmethacrylate was reacted with a copolymer comprising 80 parts of1,1,2H,2H-heptadecafluorodecyl acrylate, 80 parts ofIH,1,5Hoctafluoropentyl acrylate and 20 parts of acrylic acid, giving anacryloyl group-containing resin having a number average molecular weightof about 19,000 and an unsaturation degree of 1.3 which was dried in thesame manner as in Preparation Example 4, producing a resin having asolids content of 100%.

PREPARATION EXAMPLE 7 Preparation of component (i)-VII

In the same manner as in Preparation Example 4, 32 parts of2-hydroxyethyl methacrylate and 2 parts of ptoluenesulfonic acid werereacted with a copolymer comprising 170 parts of1,1,2H,2H-heptadecafluorodecyl acrylate and 20 parts of acrylic acid at130° C for 3 hours, whereby an acryloyl group-containing resin wasobtained with a number-average molecular weight of about 14,500 and anunsaturation degree of 1.0 and was dried in the same manner as inPreparation Example 4, producing a resin having a solids content of100%.

PREPARATION EXAMPLE 8 Preparation of component (i)-VIII

A 2l 4-necked flask was charged with 60 parts of methyl isobutyl ketoneand 60 parts of metaxylenehexafluoride and the mixture was heated to110° C. Added dropwise thereto were 170 parts of1,1,2H,2Hheptadecafluorodecyl acrylate, 10 parts of 2-hydroxyethylmethacrylate and 6 parts of t-butylperoxy-2-ethyl hexanoate through adropping funnel over a period of 3 hours after which the mixture wassubjected to aging for 1 hour. Then added dropwise thereto were 1 partof t-butylperoxy-2-ethyl hexanoate and 13 parts of methyl isobutylketone over a period of 1 hour. Thereafter the mixture was subjected toaging for 7 hours, giving a copolymer having a number-average molecularweight of about 15,000. To the copolymer thus obtained were added 22parts of a reaction product of tolylene diisocyanate and 2-hydroxyethylacrylate in equimolar amounts, and 0.1 part of hydroquinone and themixture was subjected to reaction at 100° C. for 3 hours, producing anacryloyl group-containing resin having a number-average molecular weightof 16,500 and an unsaturation degree of 0.38 The resin solution thusprepared was dried at 40° C. under reduced pressure to remove thesolvent, giving a resin having a solids content of 100%.

PREPARATION EXAMPLE 9 Preparation of component (i)-IX

Seventy-seven parts of a reaction product of isophorone diisocyanate and2-hydroxyethyl acrylate in equimolar amounts was reacted in the samemanner as in Preparation Example 8 with a copolymer comprising 150 partsof 1,IH,3H-tetrafluoropropyl acrylate and 30 parts of 2-hydroxyethylmethacrylate, giving an acryloyl group-containing resin having anumber-average molecular weight of about 21,500 and an unsaturationdegree of 1.0 which was dried in the same manner as in PreparationExample 8, producing a resin having a solids content of 100%.

PREPARATION EXAMPLE 10 Preparation of component (i)-X

In the same manner as in Preparation Example 8, 20 parts of2-hydroxyethyl acrylate was reacted with a copolymer comprising 160parts of 1,1,5H-octafluoropentyl acrylate and 60 parts of a reactionproduct of isophorone diisocyanate and 2-hydroxyethyl methacrylate inequimolar amounts, giving an acryloyl group-containing resin having anumber-average molecular weight of about 12,000 and an unsaturationdegree of 0.71 which was dried in the same manner as in PreparationExample 8, producing a resin having a solids content of 100%.

EXAMPLES 1 to 10 AND COMPARISON EXAMPLES 1 to 9

The components as shown below in Table 1 were mixed together, givingcurable compositions in Examples 1 to 10 and Comparison Examples 1 to 9.

                                      TABLE 1                                     __________________________________________________________________________                      Example     Comparison Example                              Composition       1   2   3   1   2  3                                        __________________________________________________________________________    Component (i)                                                                 Component (i)-I   100         100                                             Component (i)-II      100                                                     Component (i)-III         100                                                 Comparison resin-I                100                                         Comparison resin-II                  100                                      Component (ii)                                                                1H,1H,2H,2H--heptadecafluorodecyl                                                               100 140            100                                      acrylate                                                                      1H,1H,5H--octafluoropentyl acrylate                                                                     70                                                  UV-7000B              10                                                      Styrene (diluent)             100                                             Metaxylenehexafluoride (diluent)  30                                          Photopolymerization initiator                                                 Darocur-1173      4   5       4      4                                        Irgacure-651              4                                                   __________________________________________________________________________                      Example     Comparison Example                              Composition       4  5  6  7  4   5  6                                        __________________________________________________________________________    Component (i)                                                                 Component (i)-IV  100         100                                             Component (i)-V      100                                                      Component (i)-VI        100                                                   Component (i)-VII          100                                                Comparison resin-III              100                                         Comparison resin-IV                  100                                      Component (ii)                                                                1H,1H,2H,2H--heptadecafluorodecyl                                                               100                                                                              140   100       100                                      acrylate                                                                      1H,1H,5H--octafluoropentyl acrylate                                                                   70                                                    UV-7000B             10                                                       Styrene (diluent)             100                                             Metaxylenehexafluoride (diluent)  30                                          Photopolymerization initiator                                                 Darocur-1173      3  4     4  3      4                                        Irgacure-651            5                                                     __________________________________________________________________________                      Example     Comparison Example                              Composition       8   9   10  7   8  9                                        __________________________________________________________________________    Component (i)                                                                 Component (i)-VIII                                                                              100         100                                             Component (i)-IX      100                                                     Component (i)-X           100                                                 Comparison resin-V                100                                         Comparison resin-VI                  100                                      Component (ii)                                                                1H,1H,3H--tetrafluoropropyl                                                                     100                100                                      acrylate                                                                      1H,1H,2H,2H--heptadecafluorodecyl                                                                   150                                                     acrylate                                                                      1H,1H,5H--octafluoropentyl acrylate                                                                     50                                                  Styrene (diluent)             100                                             Metaxylenehexafluoride (diluent)  30                                          Photopolymerization initiator                                                 Darocur-1116          5                                                       Darocur-1173      4       2   4      4                                        __________________________________________________________________________

The values shown above in Table 1 are all intended to be expressed byparts. "UV-7000B" is a trademark for an acrylic urethane oligomermanufactured by Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha, Japan andhaving a number-average molecular weight of 3,000 and an unsaturationdegree of 1.2. "Darocur-1173" is a trademark for a photopolymerizationinitiator manufactured by E. Merck, West Germany and containingα-hydroxyisobutyl-phenone as an active component. "Irgacure-651" is atrademark for a photopolymerization initiator manufactured by Ciba-GeigyCorp., Switzerland and containing 2,2-dimethoxy-2 phenylacetophenone asan active component. "Darocur-1116" is a trademark for aphotopolymerization initiator manufactured by E. Merck and containing4'-isopropyl-2-hydroxy-2-methyl-propiophenone as an active component.The term "comparison resin-I" denotes a resin with a number-averagemolecular weight of about 16,000 prepared in the same manner as inPreparation Example 1 with the exception of using methyl methacrylate inplace of the glycidyl acrylate used in Preparation Example 1 andomitting the reaction with acrylic acid. The term "comparison resin-II"denotes a resin with a number average molecular weight of about 15,000and an unsaturation degree of 1.0 prepared in the same manner as inPreparation Example 1 with the exception of using 2-ethylhexyl acrylatein place of the 1,1,2H,2H-heptadecafluorodecyl acrylate used inPreparation Example

The term "comparison resin-III" denotes a resin with a number-averagemolecular weight of about 15,000 prepared in the same manner as inPreparation Example 4 with the exception of using methyl methacrylate inplace of the acrylic acid used in Preparation Example 4 and omitting thereaction with glycidyl methacrylate. The term "comparison resin-IV"denotes a resin with a number average molecular weight of about 14,000and an unsaturation degree of 1.1 prepared in the same manner as inPreparation Example 4 with the exception of using 2-ethylhexyl acrylatein place of the 1,1,2H,2Hheptadecafluorodecyl acrylate used inPreparation Example 4. The term "comparison resin-V" denotes a resinwith a number-average molecular weight of about 16,000 prepared in thesame manner as in Preparation Example 8 with the exception of usingmethyl methacrylate in place of the 2-hydroxyethyl acrylate used inPreparation Example 8 and omitting the subsequent reaction. The term"comparison resin-VI" denotes a resin with a number-average molecularweight of about 16,500 and an unsaturation degree of 0.38 prepared inthe same manner as in Preparation Example 8 with the exception of using2-ethylhexyl acrylate in place of the 1,1,2H,2H-heptadecafluorodecylacrylate used in

PREPARATION EXAMPLE 8.

Each of the curable compositions obtained in Examples 1 to 10 toComparison Examples 1 to 9 was applied to a core of quartz glass havinga diameter of 200 μm (with a refractive index of 1.458 as measured at20° C. with sodium D-line) by a die coater to form therearound a layerof the thickness as shown below in Table 2 and curing the layer byirradiation of UV rays from a high-pressure mercury lamp at the dose asindicated in Table 2, whereby a cladding was formed from which anoptical fiber was subsequently produced.

The refractive index of the cladding, NA and transmission loss beforeand after a test for cold resistance and heat resistance were measuredin respect of the optical fiber thus obtained. The refractive index ofthe cladding, NA and transmission loss before and after the test forcold resistance and heat resistance were determined by the followingmethods.

REFRACTIVE INDEX OF CLADDING

Each test composition was applied to a glass plate to form a layer ofabout 50 μm thickness and cured by irradiation of UV rays. The layer wasseparated and the refractive index of the layer was measured by an Abberefractometer. NA was determined by the result thus obtained.

Transmission loss

Light rays from a laser diode were introduced via an input device intoone end of an optical fiber having a length of slightly more than 1 km.The electric power (Po) of light rays received at the other end of theoptical fiber was determined. The optical fiber was cut at a position 1km away as measured from the egress end of the optical fiber toward theingress end thereof. The electric power of light rays received at thecut position was taken as the power of incident rays (Pi) to betransmitted from the cut position toward the egress end thereof. Thetransmission loss was given by the following equation.

    α=-(10/L)·log.sub.10 (Po/Pi)

wherein α is a transmission loss (dB/km) and L is a length (km) of theoptical fiber.

Test for cold resistance and heat resistance

The optical fiber was left to stand at -30° C. for 12 hours and then at80° C. for 12 hours, and this operation was taken as one cycle. Twentycycles were repeated for each test fiber. Table 2 below shows theresults.

                                      TABLE 2                                     __________________________________________________________________________                  Example   Comparison Example                                                                         Example     Comparison Example                         1  2  3   1    2   3   4  5  6  7  4    5   6                   __________________________________________________________________________    Thickness of cladding (μm)                                                               50 10 15  50   50  50  60 10 20 60 60   50  50                  UV radiation dose                                                                           150                                                                              150                                                                              300 600      300 150                                                                              120                                                                              300                                                                              150                                                                              600      300                 (mJ/cm.sup.2)                                                                 Test Results                                                                  Refractive index of cladding                                                                1.40                                                                             1.41                                                                             1.38                                                                              1.49 1.43                                                                              1.46                                                                              1.40                                                                             1.41                                                                             1.38                                                                             1.41                                                                             1.49 1.43                                                                              1.46                NA            0.41                                                                             0.37                                                                             0.47     0.28    0.41                                                                             0.37                                                                             0.47                                                                             0.42    0.28                    Transmission loss (dB/km)                                                                   4.5                                                                              4.5                                                                              5.0 NTP* 8.0 NTP 5.2                                                                              5.0                                                                              5.5                                                                              5.5                                                                              NTP* 7.0 NTP                 Before test for cold and heat                                                 resistance                                                                    After test for cold and heat                                                                5.0                                                                              5.0                                                                              6.0 NTP  20.0                                                                              NTP 5.5                                                                              5.5                                                                              6.5                                                                              6.0                                                                              NTP  21.0                                                                              NTP                 resistance                                                                    __________________________________________________________________________                                           Example     Comparison Example                                                8   9   10  7   8   9                  __________________________________________________________________________                             Thickness of cladding (μm)                                                               50  10  15  50  50  50                                          UV radiation dose                                                                           150 150 300 600     300                                         (mJ/cm.sup.2)                                                                 Test Results                                                                  Refractive index of cladding                                                                1.41                                                                              1.42                                                                              1.39                                                                              1.49                                                                              1.43                                                                              1.46                                        NA            0.37                                                                              0.33                                                                              0.44    0.28                                            Transmission loss (dB/km)                                                                   4.0 4.0 4.5 NTP*                                                                              8.0 NTP                                         Before test for cold and heat                                                 resistance                                                                    After test for cold and heat                                                                4.5 4.5 5.0 NTP 20.0                                                                              NTP                                         resistance                                           __________________________________________________________________________     Note: NTP = No transmitting properties                                   

Among the test fibers as shown above in Table 2, those obtained inComparison Examples 2, 5 and 8 were dried at 50° C. for 30 minutesinstead of exposure to UV radiation.

Table 2 shows that the optical fibers containing the claddings preparedfrom the curable compositions of the present invention were found tohave excellent properties because these optical fibers had great NAvalues and thus high intensity levels of optical signals, involvedmarkedly small amounts of transmission loss and slight degrees ofreduction of transmitting properties after the test for resistances tocold and heat, and were able to transmit optical signals with a highefficiency over a long distance.

EXAMPLE 11

One hundred parts of 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate and 5parts of 1,6-hexanediol diacrylate were mixed and dissolved in 100 partsof the resin obtained in Preparation Example 4 and them 100 parts oftitanium dioxide was dispersed in the solution, giving a white enamel.

The coating composition thus obtained was applied to a plate of acrylicresin to a thickness of 50 μm and cured by irradiation of electron beamsat a dose of 5 Mrad at 300 Kev. The layer thus formed was subjected toaccelerated weathering test by a sunshine weatherometer and showed goodresults in respect of gloss retention percentage and discoloration.

EXAMPLE 12

Ninety-eight parts of 1,IH,2H,2H-heptadecafluorddecyl acrylate, 2 partsof 1,6-hexanediol diacrylate and 80 parts of titanium iioxide were mixedand dispersed in 100 parts of the resin obtained in Preparation Example8, giving a white enamel.

The white enamel thus obtained was applied to a plate of ABS(acrylonitrile butadiene styrene) to a thickness of 40 μm, and was curedby irradiating electron beams at a dose of 6 Mrad at 300 Kev, providingthe plate coated with the white layer.

The coated plate was subjected to accelerated weathering test by asunshine weatherometer for 2,000 hours. The coated plate was found tohave a high gloss retention percentage (more than 90%) and presentedaesthetically acceptable appearance.

EXAMPLE 13

A resin varnish comprising 100 parts of the resin obtained inPreparation Example 8 and 80 parts of 1,1,5H-octafluoropentylmethacrylate was applied to a PET (polyethylene terephthalate) film of25 μm thickness to a thickness of 3 μm and was cured by irradiation ofelectron beams at a dose of 5 Mrad at 300 Kev.

The film thus obtained had a low refractive index and thus an increasedtransparency, 92% sunlight permeability, whereas a PET film was 85% inthis respect.

EXAMPLE 14

Six parts of "Irgacure 184" (trademark for a photopolymerizationinitiator manufactured by Ciba-Geigy Corp., Switzerland, containing asan active component 1-hydroxy-1-cyclohexylacetophenone) was added to aresin varnish comprising 100 parts of the resin obtained in PreparationExample 9 and 100 parts of 1,1,5Hoctafluoropentyl methacrylate, giving aUV radiation curable fluorine-containing coating composition. Thecoating composition thus prepared was applied to an ABS plate to athickness of 20 μm, and cured by irradiation of UV rays from ahigh-pressure mercury lamp at a dose of 200 mJ./cm².

The layer thus formed was so low in surface tension as to facilitate theremoval of ice. To prove the possession of this property, ice was formedon the surface of the layer to determine the bonding power, which wasfound to be 1.2 kg/cm² and to display a good releasability. On the otherhand, a releasability obtained from ice formed directly on an ABS platewas as poor as 4.2 kg/cm².

EXAMPLE 15

The coating composition obtained in Example 14 was applied to a cottonfabric piece and cured by irradiation of UV rays (from a coldmirror-type high pressure mercury lamp). The coated cotton fabric pieceexhibited a good water repellency whereas an untreated cotton fabricpiece showed a low water repellency.

EXAMPLE 16

The resin varnish obtained in Example 13 was applied to a transparentvinyl chloride film to a thickness of 3 μm by a roll coater and cured byirradiation of electron beams at a dose of 3 Mrad at 300 Kev. The coatedfilm was found to have a percent sunlight permeability improved by 10%over an untreated film and a percent heat dispersibility enhanced by 7%thereover.

We claim:
 1. A curable composition for forming a cladding for an opticalfiber, said curable composition consisting essentially of(i) apolymerizable double bond-containing resin prepared by reacting acopolymer comprising, as comonomers, (a) a fluoroalkyl acrylate ormethacrylate represented by the formula (I)

    CH.sub.2 ═(R)--COO(CX.sub.2).sub.m (CF.sub.2)n.sup.X

wherein R is methyl or hydrogen, X is fluorine or hydrogen, m is 1 or 2and n is an integer of 1 to 12, and (b) a vinyl monomer containing afunctional group for introducing a polymerizable double bond with acompound containing a functional group reactive with the functionalgroup of the vinyl monomer and a polymerizable double bond to introducethe polymerizable double bond into the side chain of the copolymer, and(ii) a fluoroalkyl acrylate or methacrylate of the formula (I).
 2. Acurable composition according to claim 1 wherein the resin as thecomponent (i) has an unsaturation degree of about 0.2 to about 3.0.
 3. Acurable composition according to claim 1 wherein the component (i) is apolymerizable double bond containing resin prepared by reacting acopolymer comprising a monomer of the formula (I) and an epoxygroup-containing or a hydroxyl group-containing vinyl monomer as thecomonomers with a carboxyl group-containing vinyl monomer to esterifythe epoxy group or hydroxyl group and the carboxyl group.
 4. A curablecomposition according to claim 1 wherein the component (i) is apolymerizable double bond-containing resin prepared by reacting acopolymer comprising a monomer of the formula (I) and carboxylgroup-containing vinyl monomer as the comonomers with an epoxygroup-containing or hydroxyl group-containing vinyl monomer to esterifythe carboxyl group and the epoxy group or hydroxyl group.
 5. A curablecomposition according to claim 1 wherein the component (i) is apolymerizable double bond-containing resin prepared by reacting acopolymer comprising a monomer of the formula (I) and a hydroxylgroup-containing vinyl monomer as the comonomers with a hydroxylgroup-containing vinyl monomer via a polyisocyanate compound to form aurethane linkage.
 6. A curable composition according to claim 1 whereinthe component (i) is a polymerizable double bond-containing resinprepared by reacting a copolymer comprising a monomer o the formula (I)and an isocyanate group-containing vinyl monomer as the comonomers witha hydroxyl group-containing vinyl monomer to form a urethane linkage. 7.A curable composition according to claim 1 which comprises about 5 toabout 95% by weight of the component (i) and about 5 to about 95% byweight of the component (ii), based on the total weight of thecomponents (i) and (ii).
 8. A curable composition according to claim 8which comprises about 20 to about 80% by weight of the component (i) andabout 20 to about 80% by weight of the component (ii), based on thetotal weight of the components (i) and (ii).
 9. A curable compositionaccording to claim 1 which further contains a photopolymeiizationinitiator.